The present invention relates to a graphic display apparatus for a multi-window graphic displaying system comprises a frame memory including double buffers for storing pixel data of display frames, first memorizing means for storing a successive frame number allocated to each pixel in each one of the display frames of which each set of pixel information is successively displayed and renewed, second memorizing means for storing window identifiers, each one of the identifiers being allocated in advance to each one of the multi-windows to be displayed, a table for storing the allocated frame numbers, information of designating one of buffers in the double-buffer and background color information, for each one of the multi-window, and means for comparing each one of the window identifiers and each one of the frame numbers read out from the first and second memorizing means, with each one of the window identifiers and each one of the frame numbers stored in the table, respectively, and for deciding pixel data to be displayed, based on results of the comparison, whereby it is not necessary to clear pixel data of the buffers for storing pixel data in each frame rendering, and the pixel data overwritten on the buffers need not to be cleared until the frame numbers overflow the first memorizing means.